U.S. Patent Application Publication No. 2009/0262331 discloses a crack detection system comprising optical fiber bundles, light detectors and a light source. The optical fiber bundles may be located on an outer surface of an engineering structure, such as a wind turbine rotor blade. Light pulses are provided to the optical fiber bundles. If a crack forms in the blade, one or more fiber bundles may become damaged causing light to be reflected back toward one or more corresponding light detectors. If the fiber bundles are not damaged, the pulsed light will travel through the fiber bundles and exit out an opposite end. In a further embodiment, the detectors are located at ends of the fiber bundles opposite the ends near the light source. If a fiber bundle becomes damaged due to a crack forming in the blade, a corresponding light detector will sense a decrease in the amount of light passing through the fiber bundle.